An antilock braking system (ABS) is a device to avoid locking of wheels. For example, a technique for determining whether a road surface on which a motorcycle is travelling has changed to a road surface with a high frictional coefficient from a road surface with a low frictional coefficient (whether a μ jump has occurred) is known in, for example, Patent Literature Document 1.
In the brake fluid pressure control of Patent Literature Document 1, an estimated vehicle body deceleration in a previous instance (previous control cycle) is compared to an estimated vehicle body deceleration in the current instance (current control cycle) to determine whether or not the μ jump has occurred.
In order to accurately determine the μ jump using the estimated vehicle body deceleration, however, high accuracy is also required to the estimation of the vehicle body deceleration. Thus, the processing may become complicated. In view of this, there is a demand for a technique that can accurately determine the μ jump with a simple method.